Molecular Genetics of Amino Acid Biosynthesis in Arabidopsis

拟南芥的agravitropic突变体，eir 1和EIR 1基因的分析，表明它是极性运输模型预测的泵。EIR1蛋白只在植物的根部表达，与某些细菌的外排泵有相似之处。将进行实验，为EIR1在极性运输中的功能提供直接证据。增强和抑制外排的EIR1基因的突变体将在酵母中产生，该系统提供了一种独特的工具来探测植物中的该途径。运输实验将直接测量吲哚化合物在酵母中的流出。EIR1在吲哚乙酸（IAA）从根尖到伸长区的不对称运输中的作用将通过确定EIR1在根细胞质膜中是否存在不对称定位来测试。对eir1的抑制子和增强子的基因筛选应该能识别出传递向地性信号的上游和下游基因。对EIR旁系同源物的其他家族成员的分子分析将确定这些是否是负责生长素对其他组织中向性的影响的IAA泵。将克隆这些基因，并将在这些EIR1旁系同源物中含有显性负突变的转基因植物（在酵母测定中验证）用于构建转基因植物，然后分析其向性缺陷。将使用从已经开发的筛选中获得的突变体构建细胞扩增的遗传途径。其他旨在描绘侧根形成途径的实验涉及克隆编码ALF4的基因。af1突变体通过内源和外源IAA阻断侧根的形成。此外，本论文还介绍了一种新的抗盐转基因植物的构建方法，旨在明确植物生长素（IAA）促进植物向性的信号转导途径。在向地性中，根向地心弯曲。极性运输假说假定有一种外排转运蛋白，它将IAA从根尖泵到离地心最近的根部。在那里，IAA抑制细胞的伸长，而在相反侧的细胞伸长，结果是根向下弯曲并朝那个方向生长。

Analysis of the agravitropic mutant of Arabidopsis thaliana, eir1 and the EIR1 gene, suggests that it is the pump predicted by the polar transport model. The EIR1 protein, expressed only in the root of the plant has similarities to some bacterial efflux pumps. Experiments to provide direct evidence for the function of EIR1 in polar transport will be done. Mutants of the EIR1 gene that enhance and inhibit efflux will be generated in yeast, a system which provides a unique tool to probe this pathway in plants. Transport experiments will measure the efflux of indolic compounds directly in yeast. The role of EIR1 in asymmetric transport of indol acetic acid (IAA) from the root tip to the elongation zone will be tested by determining whether there is asymmetric localization of EIR1 in the plasma membrane of root cells. Genetic screens for suppressors and enhancers of eir1 should identify the upstream and downstream genes that transduce the signal for gravitropism. Molecular analysis of the other family members of EIR paralogs will determine whether these are the IAA pumps responsible for the effects of auxin on tropisms in other tissues. These genes will be cloned and transgenic plants containing dominant negative mutations in these EIR1 paralogs (validated in a yeast assay), will be used to construct transgenic plants, which will then be analyzed for tropism defects. A genetic pathway for cell expansion will be constructed using mutants obtained from a screen, which has been developed. Other experiments designed to delineate the pathway of lateral root formation involve cloning the gene encoding ALF4. af1 mutants block lateral root formation both by endogenous and exogenous IAA. In addition, a novel approach is described to engineer transgenic plants resistant to high salt.The goal of this work is to identify the signal transduction pathway(s) by which the plant hormone auxin (or IAA) promote plant tropisms. In gravitropism, the root bends towards the center of the earth. The polar transport hypothesis posits an efflux transporter that pumps IAA up from the root tip to the side of the root closest to the center of the earth. There the IAA inhibits the elongation of the cells, whereas those on the opposite side elongate, with the result that the root bends down and grows in that direction.